In a controversial study released last year, an American criminal justice professor explored a simple question: Are suicide bombers motivated by religious ideology—or do they just suffer from depression?

Adam Lankford, a professor from the University of Alabama, concluded that many suicide terrorists weren't ideologues at all—but were, in fact, classically suicidal. He cited Israeli scholarly research of would-be Palestinian bombers: Forty percent of them exhibited suicidal tendencies; 13 percent had already attempted suicide, unrelated to terrorism. Lankford went on to mention a 9/11 hijacker who wrote a final note to his wife and lamented how he never lived up to her expectations. Lankford described other terrorists in Palestine and Chechnya who were in poor health, recently divorced, or financially insolvent in the months prior to an attack. He also talked about the terrorist recruiters who admitted to looking for the "sad guys" for martyrdom.

When it was published, the study was widely attacked in the academic world, by those who felt that Lankford's argument, a cherry-picked synthesis of existing studies, obscured the larger point of any one study, which was, more times than not, about the zealotry of terrorists, and their commitment to death, if it came to that. But even in the critics' own studies this was often the case.

The most profound revelation in Lankford's work is not only a superb parry for his critics but especially relevant now, in a post-Osama world: The idea that terrorist recruiters know, and have known, exactly the sort of guy they need for suicide terrorism. They may espouse the glories of martyrdom, but martyrs aren't always zealots. Sad guys from bleak neighborhoods sometimes do just fine, too.

The question these days, now that bin Laden is dead, shouldn't be: Will al Qaeda be able to recruit new members? It should instead be: Which kind of members will it recruit? Or, put more succinctly: How many more sad guys will it need to fill its ranks?

And when al Qaeda can't find people who are ostensibly depressed, the cell has broken them until they are.

It's relying on them a lot as it stands. C. Christine Fair, a scholar at Georgetown and the author of this United Nations report [PDF] on terrorism, found al Qaeda recruiters in Afghanistan hitting up heroin addicts to carry out its suicide attacks. And when al Qaeda can't find people who are ostensibly depressed, the cell has broken them until they are. Fair finds one suicide bomber who was told that if he did not carry out the mission, his head would be chopped off and he would go to Hell. Fair tracks down young men who were kidnapped by al Qaeda higher ups as teenagers, beaten daily, the abuse a preparation for suicide attacks, until there was no point in living. The young men now say they're ready to die.

This cruelty isn't limited to men, either. An al Qaeda operative in Iraq, a woman by the name of Samira Jassim, was most commonly known as The Mother of Believers, until her arrest in 2009. Al Qaeda soldiers would send the women they raped to Jassim, She would then use the shame and anger that accompanies such a violation against the abused, telling them that the only way to redeem their lives was to end it, in a suicide attack. Twenty-eight women did.

Don't expect al Qaeda to quit using such tactics now. Osama bin Laden was a charismatic leader who could convey his very particular brand of radicalism to an international audience. His likely successor, Ayman al-Zawahri, is cold, plodding, and officious. Impressionable youths will find very little to be impressed by. And, besides, they may have moved on. The demonstrations of this Arab Spring have been a fight for democracy, not theocracy. That likely hurts al Qaeda as much as bin Laden's death. Then there's this Pew Center study, which shows suicide attacks losing credibility among potential attackers. Together, this all might very well force al Qaeda to look harder still for terrorists, and, when they can't find them, if recent history is any guide, to "make" even more.

"Yeah, I think there's something to that idea," Lankford tells The Daily Beast. He is at work on his fourth study now on the role that suicidality plays in suicide attacks. Still, Lankford is quite taken with the notion of what happens when a zealous organization reaches the point of diminished returns. "It seems hard to imagine that kids are going to get excited and want to join a terrorist organization," he says. "In other words, if you're an ideologue, you'd have done that already." In the draft he's just finished for his latest study, which has yet to be accepted, Lankford writes about al Qaeda's coercion of recruits. The cells are now offering young men jewelry or motorcycles or sometimes just flat-out cash—the sort of Western materialism that the group's founder abhorred.

But only by any and all means will the group live on.

Paul Kix is a senior editor at Boston magazine and a contributing writer at ESPN: the Magazine. His work has appeared in, among other places, New York, Salon, and Men's Journal.